In the following description, like portions and like members are denoted by the same reference numerals throughout the drawings, and their repeated descriptions will not be provided.
An air conditioner mounted on a vehicle (hereinafter referred to as a “vehicular air conditioner”) is known (see Patent Document 1). As shown in FIG. 9, such a vehicular air conditioner includes a compressor (1); a condenser (2) for cooling refrigerant compressed by the compressor (1); an expansion valve (pressure reducer) (3) for reducing the pressure of the refrigerant cooled by the condenser (2); an evaporator (4) for evaporating the pressure-reduced refrigerant; a double-tube heat exchanger (5) which has a high-temperature-side refrigerant passage (6) and a low-temperature-side refrigerant passage (7) and in which heat exchange occurs between refrigerant of high temperature and high pressure (refrigerant flowing through the high-temperature-side refrigerant passage (6) after flowing out of the condenser (2)) and refrigerant of low temperature and low pressure (refrigerant flowing through the low-temperature-side refrigerant passage (7) after flowing out of the evaporator (4)); and a liquid reservoir (8) for storing the refrigerant of high temperature and high pressure (the refrigerant flowing out of the condenser (2)) in a stage before the refrigerant is reduced in pressure by the expansion valve (3) and for separating liquid-phase and gas-phase portions of the refrigerant from each other. The liquid reservoir (8) is provided between the condenser (2) and the intermediate heat exchanger (5). The refrigerant enters the liquid reservoir (8) before flowing into the high-temperature-side refrigerant passage (6) of the double-tube heat exchanger (5). After flowing out of the liquid reservoir (8), the refrigerant flows into the high-temperature-side refrigerant passage (6) of the double-tube heat exchanger (5).
In the vehicular air conditioner described in Patent Document 1, the refrigerant of high temperature and high pressure compressed by the compressor (1) (see a state A in FIG. 10) is cooled in the condenser (2) (see a state B in FIG. 10). The cooled refrigerant flows into the liquid reservoir (8), where liquid phase and gas phase portions of the refrigerant are separated from each other. The refrigerant flowing out of the liquid reservoir (8) flows into the high-temperature-side refrigerant passage (6) of the double-tube heat exchanger (5). While flowing through the high-temperature-side refrigerant passage (6), the refrigerant is super-cooled by the refrigerant of relatively low temperature flowing through the low-temperature-side refrigerant passage (7) after flowing out of the evaporator (4) (see a state C in FIG. 10). The refrigerant of high pressure supper-cooled in the double-tube heat exchanger (5) is caused to adiabatically expand in the expansion valve (3), whereby the pressure of the refrigerant is reduced (see a state D in FIG. 10). The refrigerant of reduced pressure enters the evaporator (4), and cools air flowing through air-passage clearances, while flowing through the evaporator (4), whereby the refrigerant becomes gas-phase refrigerant (see a state E in FIG. 10). The refrigerant of relatively low temperature flowing out of the evaporator (4) passes through the low-temperature-side refrigerant passage (7) of the double-tube heat exchanger (5). The low-temperature-side refrigerant passing through the low-temperature-side refrigerant passage (7) of the double-tube heat exchanger (5) is heated to higher temperature (see a state F in FIG. 10) by the high-temperature-side refrigerant passing through the high-temperature-side refrigerant passage (6). The heated refrigerant is then fed to the compressor (1) and is compressed.
Incidentally, in the vehicular air conditioner described in Patent Document 1, the refrigerant flowing into the liquid reservoir (8) is in the state B of FIG. 10. In order to efficiently separate liquid-phase refrigerant and gas-phase refrigerant within the liquid reservoir (8), the liquid-phase refrigerant within the liquid reservoir (8) must be stably maintained in the liquid phase, without changing to gas-phase refrigerant. In order to stably maintain the liquid-phase refrigerant in the liquid phase, without changing it to gas-phase refrigerant, within the liquid reservoir (8), in actuality, the refrigerant flowing into the liquid reservoir (8) must be super-cooled by about 3 to 5° C. Therefore, in the vehicular air conditioner described in Patent Document 1, the refrigerant must be super-cooled by about 3 to 5° C. in the condenser (2). However, in the case where the refrigerant is super-cooled in the condenser (2), the following problem arises. In an assumed case where the area of the effective core section of the condenser (2) is unchanged, the area of a portion contributing to condensation of the refrigerant must be reduced, whereby the refrigerant condensation efficiency of the condenser (2) drops. In addition, when the refrigerant condensation efficiency of the condenser (2) drops, the amount of refrigerant circulating through the vehicular air conditioner must be reduced, which results in deterioration of cooling capacity. Also, in the case where the refrigerant is super-cooled in the condenser (2), super-cooling efficiency greatly varies depending on the velocity of wind which the condenser (2) receives, wind velocity distribution, and outside air temperature.